1. Field of the Invention
This invention relates to a process for mounting a metal part in a composite material part that belongs in particular to an aircraft subassembly.
2. Description of the Related Art
Aircraft is defined as an airplane, a helicopter, any aerodyne craft that can operate within the Earth's atmosphere, or any space vehicle.
An aircraft comprises numerous parts that form various sub-assemblies that are assembled with one another.
These parts and these sub-assemblies are made integral with one another by means of various connections that are rigid or that allow certain degrees of freedom.
Some of these sub-assemblies are subjected to significant mechanical stresses and to a large number of cycles of use over the life of an aircraft.
For example, landing gear of an aircraft generally consists of numerous parts and sub-assemblies whose kinematics allows said gear to extend into/retract from a compartment box that is provided inside the fuselage or wings. This kinematic assembly, whereby axles support the wheels as far as the actuating cylinder, must withstand and damp numerous landing impacts.
Consequently, the design of the various parts and the implementation of the connections between said parts that are involved in the assembly of these particularly stressed sub-assemblies require the use of resistant materials that are manufactured and machined with great precision and optimized processes that leave no parameter to chance.
However, despite improvements made in the modeling of the properties of the materials and connections between parts and the processing of new materials, certain components and certain connections become damaged and should be replaced during maintenance operations, sometimes for repair work and sometimes for preventive maintenance in anticipation of fatigue in a material or wear and tear on a contact surface.
Various processes of the prior art have therefore been developed so as to improve the mechanical characteristics and to extend the service life of the parts and connections of the aircraft sub-assemblies.
It is possible to cite, for example, the connections that comprise at least one hole that is made in one part.
A first process of the prior art that aims at improving the mechanical characteristics of the material around a hole of a metal part rests on the creation of residual compression stresses around said hole, which makes it possible to increase fatigue life and corrosion resistance.
More specifically, this first process, which is known as “cold-working,” consists in cold-working the material; said cold-working is accomplished using a burnisher and a slit ring. Said slit ring is withdrawn after going through the burnisher and embossing the material, and then the hole is rebored for final sizing.
There are also other cold expansion processes such as ringless expansion with a slit burnisher, or else by perforation.
A second process of the prior art, used in both production and maintenance, consists in permanently installing a metal ring by cold expansion in a hole of a metal part.
More precisely, this second process, called cold-expansion ringing, consists in:                expanding said metal ring in the hole using a burnisher so as to introduce residual compression stresses in the metal material around the hole, and        leaving said metal ring in the hole so as to ensure a strong mechanical interference, i.e., a tightening, whereby the residual compression stresses ensure, in the mounting of the ring, a high resistance to detachment by traction/compression and rotation.        
Of course, the metal ring can then be rebored to a specific size.
Whereby the modeling by finished elements of the properties of metal materials allow simulations that are very close to reality, the parameters for production of these two processes of the prior art are fully known and adjusted.
However, although they are widely used even now, these two processes of the prior art only make it possible to improve the mechanical characteristics and to extend the service life of a connection that comprises a hole that is made in a metal part.
Already today and even more in the future, among the secondary parts and even the primary parts of the aircraft, or parts that belong to the structure of the aircraft, increasingly parts made of composite material will replace parts made of metal material in the aircraft sub-assemblies. The problem therefore arises of reinforcing and ensuring repair possibilities of the connections comprising a hole in a composite material part of an aircraft sub-assembly, including in a part that belongs to the structure of the aircraft and is able to be greatly stressed.
A known process of the prior art that addresses this problem calls for reinforcing a hole that is made in a composite material part by mounting a metal ring in said hole.
According to this process, the mounting of said metal rings is carried out by means of an adhesive that is applied on the outside wall of said ring before it is inserted into said hole.
The sealing of a metal ring by means of an adhesive provides good resistance to detachment forces, but it cannot be considered as a mounting process that leads to long-lasting and sufficiently homogeneous performances.
In addition, the application of the adhesive on the outside wall of the ring just before its mounting and the bonding procedure are dependent on the operator, the manipulation being difficult to accomplish.
Another solution of the prior art calls for inserting the metal ring by co-curing during the production of the composite material part; this solution gives rise to costly and difficult implementation procedures.